My mom is 50 and has been smoking pot regularly since..oh...she was born, I suppose.
She tells me without any reservation that pot is no more potent these days than it was back in the 60's and 70's. Absolutely none. Just like then, you can get different "strains" or potencies depending on how much you want to pay (or not pay), but that pot today does not have a higher THC content than it did however many years ago.
http://www.drugtext.org/sub/marmyt1.html8. Marijuana is more potent today than in the past
This myth is the result of bad data. The researchers who made the claim of increased potency used as their baseline the THC content of marijuana seized by police in the early 1970s. Poor storage of this marijuana in un-air conditioned evidence rooms caused it to deteriorate and decline in potency before any chemical assay was performed. Contemporaneous, independent assays of unseized "street" marijuana from the early 1970s showed a potency equivalent to that of modern "street" marijuana. Actually, the most potent form of this drug that was generally available was sold legally in the 1920s and 1930s by the pharmaceutical company Smith-Klein under the name, "American Cannabis".
http://www.drugpolicy.org/marijuana/factsmyths/MYTH: MARIJUANA IS MORE POTENT TODAY THAN IN THE PAST. Adults who used marijuana in the 1960s and 1970s fail to realize that when today's youth use marijuana they are using a much more dangerous drug.
FACT: When today's youth use marijuana, they are using the same drug used by youth in the 1960s and 1970s. A small number of low-THC sample sized by the Drug Enforcement Administration are used to calculate a dramatic increase in potency. However, these samples were not representative of the marijuana generally available to users during this era. Potency data from the early 1980s to the present are more reliable, and they show no increase in the average THC content of marijuana. Even if marijuana potency were to increase, it would not necessarily make the drug more dangerous. Marijuana that varies quite substantially in potency produces similar psychoactive effects.
http://www.montananorml.org/facts.php3Myth: Marijuana is much more potent today than the sixties and seventies.
Fact: Improper storage and small sample sizes characterize the potency statistics from the sixties and seventies. Higher potency marijuana may be more available today than it was two decades ago because users are turning away from low quality Mexican shipments, and growing their own indoors more frequently. Higher potency does not make marijuana more or less dangerous -- users simply tend to smoke less.